I got a couple of WM-61A mic capsules to make a measurement mic. I did the Linkwitz mod to both - removed the connection from one terminal to the outside casing and connected the other terminal to the outside casing. Both mics tested the same - they took a nosedive at low frequencies, so I sealed the whole back with silicone as per Linkwitz instructions. No change.

Then I wired them both up the way they came (no Linkwitz mod, no silicone covering the back) and they both seem to measure fine at first glance with normal low frequency performance, although the high frequencies above maybe 7khz look a bit low.

Then I did the Linkwitz mod on them again, just to be sure I did it right the first time and I got the same terrible low frequency results again.